DESCRIPTION: Fibromyalgia (FM) is a disabling disorder characterized by widespread medically unexplained pain. A diagnosis of FM is accompanied by a limited prognosis and less than half of all FM patients experience adequate pain relief. FM patients are often left under treated, resulting in greater functional disability and increased health care utilization. Research Aimed at uncovering mechanisms of unexplained pain in FM is needed to guide potential treatment approaches and better understand the pathophysiology of this disorder. Brain imaging data collected in laboratory have demonstrated augmented fMRI responses to both non-painful and painful heat, and support the emerging view that abnormalities in central nociceptive processes act to maintain FM pain. Nevertheless, cognitive processes such as anticipation and attention could also affect brain responses and are known to affect chronic pain outcomes. The broad objectives are to further understanding of unexplained musculoskeletal pain in FM. fMRI is an objective measure of nociceptive processing, sensitive to sensory and cognitive manipulations. Thus, the Specific Aims of the project are to: (1) determine whether augmented central processing is unique to FM or is a consequence of chronic pain by comparing FM patients to rheumatoid arthritis patients (RA);(2) determine the influence of pain anticipation on fMRI responses to non-painful stimuli in FM patients compared to healthy and RA controls, and (3) determine the influence of attention to pain on central processing of painful stimuli in FM patients compared to healthy and RA controls. To manipulate anticipation of pain, subjects will be randomly assigned to pain and no pain conditions. To manipulate attention to pain, subjects will perform the Stroop color word task while receiving either painful or non-painful heat stimuli. The study will be conducted on two separate days. Day one will be conducted in a simulated MRI unit for psychophysical analysis of pain and performance of the Stroop. Day two will consist of functional brain imaging (fMRI) while the subjects receive either non-painful or painful heat stimuli and perform the Stroop. We posit that FM is a unique chronic pain disorder that involves dysregulated processing of sensory stimuli and that augmented brain responses will not be affected by manipulations of anticipation and attention. This will be a first important step towards understanding the mechanisms of unexplained muscle pain in FM.